1. Field of the Invention
This invention relates to medical instrumentation and, in particular, to methods for the analysis of aggregations of thrombocytes also known as blood platelets and devices utilizing this method.
2. Description of the Related Art
Blood cells are known to form aggregates in response to some physiological agents, referred to as aggregation inducers hereinbelow, such as: ADP, platelet activating factor, thrombin, collagen, thromboxane A.sub.2, and others. The ability to form aggregates makes platelets the leading factor in triggering the hemostasis mechanisms. Any disruption in the functional activity of blood platelets lead to pathological changes. Analysis of spontaneous or induced aggregation of blood platelets in response to the inducer action makes it possible to diagnose various pathological conditions associated with disruptions of the cell link of hemostasis. It is important that spontaneous aggregation of thrombocytes or large-size aggregations caused by standard action of an aggregation inducer creates the tendency for thromboses, while a decrease in or the absence of a response to such action creates a tendency to bleeding. Concentration of blood cells, particularly platelets, is also an indication of the physiological condition. Thus, a decrease in concentration of circulating platelets may occur during severe toxicosses, disseminated intravascular coagulation of blood, serious and vast injuries, irregular thrombocytopoiesis, and some other deseases. A change in the concentration of platelets during their in vivo aggregation is a diagnostic indication of the condition of the hemostasis system of a body.
Known in the art are several methods for the analysis of thrombocyte aggregation such as optical microscopy, electronic microscopy and conductometric platelet count. These methods are based on direct counting of the number of thrombocytes and determination of distribution of aggregates in accordance with size in appropriately prepared blood samples. However, methods of preparation of blood samples cause substantial errors in the results because of the action of substances, and in particular fixatives, dyes and the like upon blood cells. In addition, these methods are very labour-consuming and unsuitable for such a rapidly occurring process as aggregation of thrombocytes.
The most similar to the method according to the invention is a photometric method for the analysis of thrombocyte aggregation, comprising measuring intensity of light flux passed through a thrombocyte suspension sample. A standard platelet rich plasma is turbid because of the presence of thrombocytes in the suspension. The value of intensity of light passed through the sample is used for determining concentration of thrombocytes. When aggregates are formed, turbidity decreases, and this is used for recording aggregation. For carrying out the method, a blood sample is illuminated with a light beam, and intensity of light flux passed through the sample is recorded. A change in the light flux passed through the sample during aggregation of thrombocytes gives a typical "picture" of aggregation, and the kinetics and degree of aggregation of thrombocytes are evaluated by maximum increase in light transmission (Journal of Physiology, vol. 162, 1962, London, Born B.V.R. Quantitative Investigation into the Aggregation of Blood Platelets, p. 67).
Known in the art are apparatuses used for carrying out the above described method. They comprise a light flux source, a means for holding a blood sample and for stirring it, and a photosensitive member converting light flux passed through the blood sample into an electric signal.
Thus known in the art is an apparatus for the investigation into aggregation with an automatic ranging of an output signal in which a reference signal is in the form of an electric signal corresponding to a light transmission of an autologous sample of platelet poor plasma. The apparatus has two cell compartments, a sample of platelet rich plasma being placed in one compartment and a sample of platelet poor plasma being placed in the other compartment (U.S. Pat. Nos. 4,135,818; 3,989,382).
Also known in the art is an apparatus for measuring thrombocyte aggregation in which a means for containing a sample of thrombocytes comprises a hollow cylinder, and the sample is moved by rotating the cylinder about its axis (U.S. Pat. No. 4,066,360).
In addition, known in the art is an apparatus for investigating into blood properties making use of a light source in the form of a lamp, a cell compartment and a magnetic stirrer positioned on the bottom wall of the cell compartment. Light flux passed through the sample is converted into an electric signal in a photo receiver. This signal corresponds to intensity of the light flux. This apparatus can be used for the analysis of thrombocyte aggregation only without any modifications (U.S. Pat. No. 4,116,564).
One of disadvantages of the prior art method and of apparatuses for carrying out this method resides in the fact that it is not possible to determine size of forming aggregates by a change in light transmission of a sample of blood plasma rich in thrombocytes. This is due to the fact that optical density of a sample is not unambiguously related to the size of forming aggregates. It may occur that two samples will differ in the number of thrombocytes forming aggregates and in the size of the formed aggregates, yet the sample being of one and the same optical density. The shape of thrombocytes also substantially effect optical density. A change of thrombocytes from flat discs to round shape change optical density of a sample by 30-40%. This hampers differential diagnostics of increased activity of thrombocytes in each specific case. In addition, the dependence of reading of the prior art method on light absorption by the medium (blood plasma) makes technical implementation of the method very complicated.
The abovedescribed method and apparatuses have a certain threshold of sensitivity. This does not allow spontaneous aggregation of thrombocytes and aggregation after the action of activators in low concentrations when an average number of thrombocytes in an aggregate does not exceed 100-200. Low sensitivity hampers or even makes it impossible in a number of cases to diagnose hyperactivity of thrombocytes. Moveover, it is inducers in low concentrations that can appear in the actual vessel blood flow, and the inhibiting effect of certain medicines on the aggregation can be detected after the action of such physiological concentrations of inducers.
The optical density of a sample depends not only on particle concentration, but also on optical properties of particles proper and their environment as well as on the structure of an optical channel of the apparatus. Consequently, it is not possible to determine with adequate accuracy concentration of cells by light transmission of the sample.